I think if someone is trying to decide if they want to use a Facebook group for example or discourse, one feature you could say Facebook has is that everyone is using their real name (well most people).
I signed in to discourse with Facebook, but there is no indication I did. I’m sure not all discourse forums would want this, but for some communities it might be a bit of a built in reputation system if discourse would verify somehow that you logged in with a certain Facebook account, or Google+ account. For a community with a buy and sell section for example I can see how this would be good. For example, I’m in a couple Facebook groups exclusively that are buy and sell type of groups, but there is no way that those groups can be effective discussion groups too, as there are 1000+ members and it is just full of posts of items for sale, no real way to have categories. But there is a sort of built in trust system there, making Facebook attractive for groups like that.
I searched and part of this has been asked for, having the Google+ or Facebook profile pic become their avatar - Google Avatar - not associating?
I would even go further and have an indication in the person’s discourse profile, like a link to their Facebook account and some sort of “Verified” checkmark like the blue checkmark some twitter accounts have. Maybe you could even verify your Facebook, Google+ and Twitter if you wanted to. Anyone like that idea?
edit - Here’s some info on how to format an icon or ‘badge’ link to a profile:
facebook profile badges: https://www.facebook.com/badges/
and google+ badges: Google+ Badge | Google+ Platform for Web | Google Developers
edit - the multiple logins to one discourse has been asked for too - Allow authentication via multiple services on one account - just doesn’t seem to mention displaying in your profile that you have authenticated with multiple accounts, which I guess wasn’t the intention of that topic.